The present invention relates to methods and systems for the rapid measurement of the scattering properties of decorative and barrier coatings and plastics arrays, which in turn are indicators of the overall integrity of the coating or plastic material.
Applications of decorative and barrier coatings include finishing the exteriors of automobile and truck bodies, appliances, electronic parts, and other high-quality products. In the combinatorial discovery of coating materials for applications such as decorative and barrier coatings, the rapid evaluation of the optical quality of the coating itself is of considerable importance. Optical quality of coatings such as haze and light, or electromagnetic radiation, scattering is affected by several factors. These factors include internal haze levels during coating deposition and curing, scattering defects due to poor abrasion resistance, and crack formation during elongation, hydrolytic stability tests, and exposure to solvents. Thus, the optical quality of the coating is directly related to the coating condition and the overall integrity of the film. There is a direct correlation between the amount of scattered radiation and the quality of the coating.
A typical method for such measurements is haze determination. In this method, a relatively large area of the coating (about 1 cm2) is measured to provide values for the transmitted and diffused (scattered) radiation. Haze is calculated as the ratio of the diffuse transmitted radiation to the total transmitted radiation. This measurement method has several shortcomings that limit its applicability for the high throughput applications such as those for the screening of combinatorial libraries. These drawbacks include difficulties in obtaining reliable measurements of haze values of less than 0.5%, the need to have a relatively large coating area for measurements, impossibility in the determination of the presence of a transparent coating on the substrate, difficulties in the rapid measurement of multiple samples on non-flat substrates, impossibility of measurements of haze on opaque substrates, and difficulties in measurement automation. As a result, reliable evaluation of optical parameters of multiple small-scale transparent thin coatings presents an analytical measurement challenge. Thus, the need exists to provide a means for performing high throughput measurements.
This invention provides methodology for the measurement of both low and high levels of scattered radiation produced by decorative and barrier coatings. Measurements of low levels of scattered radiation are especially important for coatings such as those used in automotive applications. The method is based on the illumination of a coating sample with an electromagnetic radiation source and collection of only a portion of the radiation scattered from the coating. Good correlation has been found between the data obtained via the practice of this invention and such data obtained via more cumbersome and inherently limited methodology such as that set forth in ASTM D 1003, and other tests. Through the practice of the invention, a large number of coating samples, as in an array, may be analyzed for their optical quality, i.e., principally haze, either after coating and curing, and/or after subjecting such coatings samples to elongation stresses and/or abrasion and hydrolytic stability testing. An advantage of this invention is that when analyzing an array, the substrate is used as a reference for comparison of the optical quality of the substrate to that of the coating sample. In such an array, the uncoated substrate areas between the individual members of the coating array or library may be utilized as internal standards. A further advantage is the capability to analyze the standards and various abraded coating regions to determine the relative performance of a member of the combinatorial array or library.